1. Field of the Invention
The invention relates to a control system for an internal combustion engine and a control method for an internal combustion engine, and more particularly to a technique for detecting a fuel supply to a fuel tank.
2. Description of the Related Art
In a control system for an internal combustion engine, a remaining fuel amount is detected on the basis of an output of a fuel gauge provided in a fuel tank. The presence of a fuel supply to the fuel tank may then be determined as a part of engine control.
For example, Japanese Patent Application Publication No. 2007-10574 (JP-A-2007-10574) describes a breakdown diagnosis device for a fuel level gauge which outputs a voltage corresponding to a fuel level of a fuel tank. In this device, when diagnosing an abnormality in the fuel level gauge in accordance with a correlation between an output of the fuel level gauge and a fuel injection amount integrated value, a plurality of determination values of the fuel injection amount integrated value are provided in accordance with the fuel level as triggers for mediating the abnormality determination. In JP-A-2007-10574, initialization processing is performed on the fuel injection amount integrated value when fuel is supplied, as well as when a battery is cleared and when a diagnosis is completed, and therefore the presence of a fuel supply must be determined.
JP-A-2007-10574 describes a fuel supply detection method in which the presence of a fuel supply is determined on the basis of a determination as to whether or not a difference between a fuel level average value at the time of engine stoppage and a fuel level average value at the time of engine start-up exceeds a fuel supply determination value.
However, in the fuel supply detection method described in JP-A-2007-10574, the fuel level average value at the time of engine stoppage is determined as a reference value corresponding to a case in which a fuel supply is absent, and it may therefore be impossible to determine the presence of a fuel supply accurately depending on operating conditions at the start and end of a vehicle operation.
More specifically, in a case where the vehicle is stopped suddenly such that the engine is stopped rapidly, the fuel level average value at the time of engine stoppage is determined with the fuel level in an unstable condition, and it may therefore be impossible to set the reference value accurately. Furthermore, it is impossible to detect a condition in which the engine is not stopped and fuel continues to be supplied with the engine in an idling condition. Moreover, when the vehicle is caused to advance rapidly immediately after engine start-up, the fuel level of the fuel tank becomes unstable, and therefore an erroneous determination may be made.